«Zane Vincēviča-Gaile IMPACT OF ENVIRONMENTAL CONDITIONS ON MICRO- AND MACROELEMENT CONTENT IN SELECTED FOOD FROM LATVIA Summary of doctoral thesis ...»
Element bioavailability in food chain segment soil-plant is tightly associated with the solubility of chemical compounds. Elements can be taken up by plants if they are present in the soil as soluble ions in the forms of organic or inorganic complexes. In addition, not only concentration of ions but also type and chemical character of complexes formed, as well as soil properties such as organic matter content and pH are important in case of plant ability to accumulate potentially toxic elements (Gardea-Torresdey et al., 2005; Inaba and Takenaka, 2005; Peralta-Videa et al., 2009).
Element bioavailability in upper segments of food chain food-human is especially important concerning essential elements, as well as potential pollutants and it is dependent not only on chemical properties of compound but also on composition of nutrition and individual 12 health conditions. Total element content does not reveal element bioavailability but provisional assessment can be based on calculated bioavailability extent (usually expressed in %) based on widely done in vivo and in vitro studies (ATSDR, s.a.), that can be applicable for the estimation of food nutritional value and food safety, if total element quantitative content is available.
1.3. Recent studies of micro- and macroelement analysis in Latvia
The assessment of recent research studies of element concentration investigation in Latvia was based on the information available in the main international scientific databases Scopus, Science Direct, Springer Link and ISI Web of Knowledge for the time period 2000Element content in environmental and biological samples has been studied by G. Čekstere with colleagues who analysed chemical composition of Riga street greenery, particularly, leaves of lime trees and environmental impacts on element content (Čekstere, 2011; Cekstere and Osvalde, 2013; Cekstere and Osvalde, 2010a; Cekstere and Osvalde, 2010b; Cekstere et al., 2008). Air pollution and element content interactions in mosses in Latvia have been studied under the guidance of professor O. Nikodemus and G. Tabors (Nikodemus et al., 2004; Tabors et al., 2004). Finnish scientist R. Salminen with colleagues (2011) also investigated element distribution in terrestrial mosses and organic soil layer in the Eastern Baltic Region. Soil element content has been investigated in details by A. Gilucis (2007) that is described in his doctoral thesis, but metal deposition in forest soils of Latvia and the influencing environmental factors has been studied by other scientists of Latvia (Brumelis et al., 2002; Kasparinskis and Nikodemus, 2012).
Another group of research widely studied involves the analysis of inland surface waters with the aim to detect element and nutrient content (Aldahan et al., 2006; Klavins et al., 2001;
Klavins et al., 2000; Kokorite et al., 2010; Stalnacke et al., 2003) and element content of lake sediment investigation (Klavins et al., 2011; Klavins and Vircavs, 2001). But latest studies are tended to bog investigation (Klavins et al., 2009b; Klavins et al., 2003; Silamikele et al., 2011). Prof. M. Kļaviņš with colleagues (2009a) has investigated heavy metal content in fish from lakes in Latvia.
Analytical approach of the analysis of elements by X-ray fluorescence techniques has been investigated under the supervision of professor A. Vīksna (Viksna et al., 2004; Viksna et al., 2001), while P. Sudmalis (2013) in his doctoral thesis was dealing with problems connected with possibilities to detect persistent organic pollutants in environment and biological samples.
Trace metal analysis in water samples from Gulf of Riga and Daugava River estuary have been done (Pohl et al., 2006; Poikane et al., 2005; Yurkovskis, 2004; Yurkovskis and Poikane, 2008). The studies on metal pollution in environment also have been done in Latvia (Kulikova et al., 2003; Muller-Karulis et al., 2003).
Only few studies in Latvia are related to food composition investigations. The information can be found about the studies of nutrient composition of American cranberries in Latvia (Osvalde and Karlsons, 2010) and potatoes (Murniece et al., 2011). F. Dimiņš (2006) in his doctoral thesis investigated composition of honey, including analysis of some element concentration.
Some studies revealing food consumption specifics in Latvia have been done (Melece, 2009; Melece et al., 2008; Pomerleau et al., 2001a; Pomerleau et al., 2001b). However, in these studies only economical aspects were taken into account in the description of food consumption habits in Latvia. The studies of nutrition regarding health issues and interconnection with environmental impacts have been done (Luse et al., 2000; Muceniece et al., 2007; Richardson et al., 2013), but these are specific investigations in the field of 13 environmental and occupational medicine where biosamples such as human blood and hair were analyzed.
Research in the field of agriculture in Latvia concerning food quality improvement are represented by some studies done by I. Alsina with colleagues who have investigated selenium impact on yield quality of lettuce (Alsina et al., 2012; Zegnere and Alsina, 2008).
However, survey of recent studies in Latvia of analysis of micro- and macroelements revealed that there is lack of information about the analysis of the content and concentration of elements in food consumed and produced in Latvia. Therefore, the importance of current research is highly valuable within the interdisciplinary fields of environmental science, chemistry, food science and health sciences.
2.1.1. Collection of food samples Locally available food samples were collected over the territory of Latvia in the time period 2009-2013. Food for sampling was selected as follows (methodology after Aras and Ataman, 2006; Ekholm et al., 2007): (I) vegetable products – unprocessed (apples, carrots, onions, potatoes) and processed (cereal meals and cereal mixtures for porridge preparation);
(II) animal products – unprocessed (bee products such as honey, pollen and bee bread; hen eggs) and processed (cottage cheese); (III) beverages – unprocessed (apple juice, birch sap) and processed (apple wine). Selection of food samples collected for analyses was based on the length of element transfer from the environment to the food, as well as possible impact factors such as seasonality, agricultural praxis or processing were taking into account. In total more than 500 food samples were analysed within the research.
Collected food samples of plant origin:
Root vegetables – onions Allium cepa (ns1=98), carrots Daucus carota (ns=81), potatoes Solanum tuberosum (ns=55) and potato peel (ns=6) (Figures 2.1., 2.2., 2.3.);
Leafy vegetables – leafy lettuce Lactuca sativa (collected over the territory of Latvia (ns=7) and grown in contaminated soil (ns=3) (Figure 2.4.);
Fruits – apples Malus domestica (ns=21) and apple peel (ns=3) (Figure 2.4.);
Cereal meals (cereal meals and cereal mixtures for porridge preparation) – cereal mixtures such as 3-grain flakes for porridge preparation (ns=10), rice products (ns=10), wheat products (ns=12) and buckwheat products (ns=11).
At the sampling the origin of samples was identified. Sampling was carried out by selecting 3-5 pieces of fresh vegetables or fruits within every single sample subsequently making mixed samples. Except for porridge cereals which were initially collected in commercial packaging, vegetables of every sample were washed, peeled, crushed with ceramic knife (Kiocera) and dried in drying oven (Labassco) at temperature 80-105 °C, depending on moisture content in samples. After drying every sample was triturated until the consistence of powder. Until analyses samples were stored in closed disposable plastic bags in dry and dark place in room temperature (Aras and Ataman, 2006).
Collected food samples of animal origin:
Bee products (Figure 2.5.) – honey (ns=80), pollen (ns=5) and bee bread (ns=5);
Cottage cheese (ns=27) of different origin (from individual dairy farms and large-scale dairy producers) collected over summer and winter seasons (Figure 2.6.);
Hen eggs (ns=33) of different origin (from organic farms, domestic farms and large-scale poultry farms), and samples (ns=24) for seasonality impact assessment from an domestic farm with known poultry breeding conditions (at Aizkraukle, Latvia) (Figure 2.7.).
Samples of animal origin such as bee products were stored in closed polypropylene vessels in dark, dry and cool place. Cottage cheese samples were dried in drying oven (Labassco) at 60 °C and stored in hermetically closed disposable bags in freezing camera at °C. Sampled eggs were washed, carefully separated by making yolk, albumen and mixed samples, and stored in hermetically closed disposable bags in freezing camera at -20 °C (Aras and Ataman, 2006).
Origin of hen eggs from domestic farms (a), organic farms (b), large-scale poultry farms (c) and samples for seasonality detection (s) Samples of beverages (Figure 2.8.) such as apple juice (ns=9), birch sap (ns=10) and apple wine (ns=5) were kept in closed polypropylene tubes in refrigerator (+4 °C) and were analysed immediately after delivering to the laboratory.
Origin of beverage samples: apple juice (s), birch sap (b) and apple wine (v) 17 2.1.2. Pretreatment of food samples prior quantitative analysis Pretreatment of food samples prior quantitative analysis involved wet mineralization. In overall, the pretreatment procedure can be described as follows: precise weight of a sample was dissolved in concentrated analytically pure HNO3 (65 % w/v, Scharlau, Penta or Merck) adding concentrated analytically pure H2O2 (30 % w/v, Merck). After hold overnight the process was accelerated by heating of solutions on a heating block (Biosan) or in a microwave digestion system (Milestone) until full sample mineralization. Sample solutions were poured into polypropylene tubes and diluted with deionised water (0.1 µS/cm, 18 MΩ/cm, Millipore) up to a certain volume. Some samples, e.g., beverages, egg samples and honey samples were analysed also without pretreatment which is technically acceptable if total reflection X-ray fluorescence spectrometry is used for element quantification (Klockenkamper, 1997).
2.1.3. Methods of quantitative analysis For detection of quantitative concentration of micro- and macroelements in food samples such quantitative methods were used: TXRF – total reflection X-ray fluorescence spectrometry (Rontec PicoTAX, Rontec GmbH), AAS – atomic absorption spectrometry (AANALYST 200, Perkin Elmer) and ICP-MS – inductively coupled plasma mass spectrometry (ELAN DRC-e, Perkin Elmer). The most appropriate method was chosen depending on specifics of a sample and spectra of detectable elements. Samples of certified reference materials such as CS-CR-2 Carrot root powder, NCS ZC73017 Apple powder, IAEA-336 Lichen, BCR-063R Skim milk powder and PT Red wine Chilian were used for verification of applied analytical methods. Pretreatment of reference samples was done in the same manner as it was described for food samples (mineralization with concentrated HNO3).
Data describing accuracy and recovery of applied analytical techniques after analysis of NCS ZC73017 Apple powder are summarized in Table 2.1.
Accuracy and recovery of applied analytical methods (TXRF, AAS and ICP-MS) detected by the analysis of certified reference sample NCS ZC73017 Apple powder
2.2.1. Preparation of soil samples In spring of 2011 five soil samples were collected in Latvia, the southwest of Vidzeme Upland (Vecpiebalga region, Taurene rural municipality, vicinity of Lode manor), considering their representativeness for soils in Latvia (Kārkliņš u.c., 2009; Kasparinskis, 2011; Nikodemus, 2011). Soil samples were collected from upper layer (H or Ap horizon, depth 0-20 cm). The type of soil samples was identified as follows: S1 – fen peat soil; S2 – sod-podzolic soil / sandy loam; S3 – sod-podzolic soil / sand; S4 – sod-podzolic soil / loamy sand; S5 – sod-podzolic soil / sandy clay loam (FAO, 2006; Kārkliņš u.c., 2009; Nikodemus, 2011; Noteikumi 804, 2005). Soil texture and other characteristic properties such as pHH2O un pHKCl, soil organic matter expressed as content of humic substances, cation base saturation, total element content were defined in laboratory using standard methodology (FAO, 2006;
Pansu and Gautheyrou, 2006).
To model the transfer of metals from soil to plants and for the bioavailability assessment soil contamination was applied treating soil subsamples with corresponding metal
a) Soil monocontamination using copper sulphate pentahydrate CuSO4×5H2O solution at five target Cu concentrations (40, 70, 100, 130 and 200 mg/kg);
b) Soil multielement contamination using such soluble salts of metals as cadmium acetate dihydrate Cd(CH3COO)2×2H2O, copper sulphate pentahydrate CuSO4×5H2O, lead (II) nitrate Pb(NO3)2 and zinc sulphate heptahydrate ZnSO4×7H2O at certain target concentrations of elements (6 mg/kg Cd, 130 mg/kg Cu, 750 mg/kg Pb and 300 mg/kg Zn).
Soil contamination procedure was applied as described in literature, i.e., calculated amount of certain contaminant was diluted in water and sprayed over the soil piles followed by complete soil homogenization (mechanical mixing) (Alexander et al., 2006; Inaba and Takenaka, 2005). In addition, the half of each portion of contaminated soils and also control soil samples were saturated with the solution of humic substances (3 g/kg; ombrotrophic bog peat: C 54,35 %, H 2,36 %, N 1,26 %, Mw 4 500 – 12 000 dal). Two weeks after contamination repeated mechanical homogenization was done. Then contaminated and control soil samples were poured into pots and used for experimental cultivation of selected food crop species: radish Raphanus sativus L. ‘Saxa 2’, leafy lettuce Lactuca sativa L. ‘Grand Rapids’ and dill Anethum graveolens L. ‘Mammut’. The study was done during the summer season of 2011 in the central part of Latvia, in a field area at Aizkraukle, Latvia.